The present invention relates to an optical switch for switching the propagation path of an optical signal and, more particularly, to an optical waveguide switch which utilizes light as control energy for triggering its switching operation.
With the development of optical fiber communication, the optical switching technology for switching an optical signal to a desired channel is now attracting attention. It is considered, in particular, that as an optical line becomes increasingly common in the subscriber's system, optical switches will be needed in vast numbers, and their miniaturization and sophistication are desired. There is also a demand for development of an integrated optical switching element for adaptation to submarine switching in a submarine optical fiber transmission system or satellite-loaded switch which is limited in space and required to be highly reliable.
To meet with such requirements, mainly two types of optical switches are now under study. The one has an arrangement in which an optical signal is once converted to an electric signal (an opto-electro conversion) and is switched by an electronic circuit as in the past, thereafter being re-converted to an optical signal (an electro-opto conversion). As a result of the recent progress of the OEIC (Opto-Electronic Integrated Circuit) technology, a four-by-four optical switch, though in a hybrid structure, has been reported. This O/E/O type optical switch which involves the conversion of an optical signal to electric form and then back to optical form is readily acceptable as a miniaturized version of a conventional optical switching device formed by discrete elements. On the other hand, however, it is considered that because of a large number of elements used this optical switch has the defects of complexity in its manufacture, low reliability and an increase in cross-talk by electromagnetic interference in the electronic circuit during high-speed operation. In addition, it is difficult, at present, to obtain an ultra high-speed electronic circuit capable of satisfactory operations at high frequencies above several giga-Hz.
The other optical switch is one that switches an optical signal without conversion to an electric signal, and this switch is termed an O/O type. However, since these optical switches rely on electric energy such as a voltage and a current for switching the optical signal, they have to perform the O/E (opto-electro) conversion of a control signal superimposed on the optical signal.